1. Field of the Invention
The present invention relates to drive systems for motor vehicle closure devices, such as windows. More particularly, the invention relates to a safety feature for a vehicle window that detects that an object has become pinched in a vehicle window as it is commanded to close and thereby reverses direction of the window to alleviate the pinched condition.
2. Description of Related Art
Power windows for motor vehicles are very common throughout the world. In a typical vehicle power window, an electric motor is used to raise or lower the window under the control of a switch operated by an occupant of the vehicle. In view of the significant convenience that they provide over manually moved windows, power windows have become a standard feature of most new motor vehicles.
Despite their widespread consumer acceptance, power windows pose a serious risk of harm to objects that are inadvertently caught between the window and the sash as the window is closed. The closing torque applied by the electric motor to the window results in substantial force that can injure an individual's limb or head left protruding through the open window. This risk is particularly serious with small children that may be enticed to use the power windows without parental supervision, and which can be severely injured if caught between the window and sash. In view of the potential danger posed by power windows, certain governmental regulations dictate the maximum amount of force that may be applied by the electric motor in closing the window.
To prevent such injuries from occurring, motor vehicles have been provided with safety systems that detect the presence of a foreign object pinched between the window and sash. Once a pinched object is detected, upward movement of the window is halted and the window is moved downward to free the object. There are two types of safety systems in common usage, including the "differential" type and the "absolute" type.
The differential type of safety system recognizes a pinched condition from a detected change in window velocity. More particularly, the window moves upward with a velocity (v) measured by a sensor that detects the rotational rate of the electric motor. Generally, the window is moved at a constant velocity (v). In a pinched condition, however, the velocity abruptly drops. The sensor can also detect changes in velocity over time (dv/dt), and the safety system thereby recognizes the pinched condition from the detected dv/dt. The differential type of safety system has a serious drawback, however, in that there is a lag between the time that the pinched condition begins and the time at which sufficient velocity information is collected to detect and reverse the pinched condition. Since the safety system periodically samples the velocity v, it is necessary for a sufficient number of samples to be collected before an accurate dv/dt value can be recognized. While this time lag is very slight and on the order of milliseconds, it should be appreciated that a significant amount of harm may have already occurred to a foreign object caught between the window and sash before the pinched condition is recognized and corrected by the safety system.
An especially serious failure mode for the differential type of safety system is the "no-clearance condition" in which an object is already in close contact with the window and sash prior to the time the window is commanded to close. Since the window was not in motion before contacting the object, dv/dt will be zero as there is no change in velocity. The electric motor will continue to apply closing force to the window against the object until the operator recognizes the pinched condition and manually changes it to reverse direction.
In contrast, the absolute type of safety system recognizes a pinched condition when the applied motor torque exceeds a predetermined limit. The torque produced by the electric motor is generally proportional to the electric current drawn by the electric motor. In a pinched condition, the presence of a foreign object between the window and sash represents a frictional force that is opposite in direction to the applied motor torque. As a result, the electric motor draws additional current to compensate for the increased frictional force. The safety system monitors the current drawn by the electric motor, and recognizes the pinched condition when the current exceeds a predetermined limit.
The absolute type of safety system would successfully detect a pinch in the no-clearance condition by the increase in motor current, and therefore is advantageous in that particular situation over the differential type of safety system. Nevertheless, there is also a time lag in the absolute type of safety system as the current level applied to the electric motor slowly increases to the threshold value. As in the differential type of safety system, this time lag may result in a significant amount of harm to a foreign object pinched by the window. Thus, both the differential type and the absolute type of safety systems do not provide entirely satisfactory solutions to the problem of detecting a pinched condition in a motor vehicle power window.
Thus, it would be desirable to provide an improved safety system for a motor vehicle power window. Such an improved safety system should have the beneficial aspects of the differential and absolute safety systems known in the art, without the serious drawbacks of these systems described above.